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I hear about cats "grenading " and getting sucked into the engine. My question is how this is possible? I thought the cats were after the exhaust manifold, so the flow is going outward. How do things get sucked back in? Thanks.
 

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There is no performance lost, but has me worried about the failing cats and grenading the motor. [\quote]
 

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It happens because Nissan, for some reason, does not use EGR valves on most of their engines. They set the exhaust cam timing to stay open a little longer than usual so it's still open during the intake stroke, thus sucking in exhaust gasses, acting like an EGR valve. The only reason Nissan is now having issues with it is because of the pre-cats mandated by the EPA. With the CAT mounted so close to the cylinder head, it causes this issue, among others. CATs break apart and particulate over time, it's normal. Nissan just needs to re-think their engine designs and include an EGR valve now. Then the problems with the engine eating the kitty should go away.

FYI, the Sentras with the QR25 engines are plauged with this problem too. Just on a greater scale.
 

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Discussion Starter #5
Yellomantis said:
It happens because Nissan, for some reason, does not use EGR valves on most of their engines. They set the exhaust cam timing to stay open a little longer than usual so it's still open during the intake stroke, thus sucking in exhaust gasses, acting like an EGR valve. The only reason Nissan is now having issues with it is because of the pre-cats mandated by the EPA. With the CAT mounted so close to the cylinder head, it causes this issue, among others. CATs break apart and particulate over time, it's normal. Nissan just needs to re-think their engine designs and include an EGR valve now. Then the problems with the engine eating the kitty should go away.

FYI, the Sentras with the QR25 engines are plauged with this problem too. Just on a greater scale.

Thanks. It makes a little more sense now.
 
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